Fabrication of Magnetic Nanostructures on Silicon Nitride Membranes for Magnetic Vortex Studies Using Transmission Microscopy Techniques

Abstract

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared on transparent membranes which are very fragile and difficult to manipulate. We present processes for the fabrication of samples with magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for Lorentz transmission electron microscopy and magnetic transmission x-ray microscopy studies. The samples are prepared on silicon nitride membranes and the fabrication consists of a spin coating, UV and electron-beam lithography, the chemical development of the resist, and the evaporation of the magnetic material followed by a lift-off process forming the final magnetic structures. The samples for the Lorentz transmission electron microscopy consist of magnetic nanodiscs prepared in a single lithography step. The samples for the magnetic x-ray transmission microscopy are used for time-resolved magnetization dynamic experiments, and magnetic nanodiscs are placed on a waveguide which is used for the generation of repeatable magnetic field pulses by passing an electric current through the waveguide. The waveguide is created in an extra lithography step.

TEM sample preparation of lithographically patterned permalloy nanostructures on silicon nitride membranes

“…However, the corresponding samples need to be prepared on electron-beam-transparent membranes, which are very fragile and can easily break during standard lithography procedures. Although a lift-off approach has been demonstrated [ 20 ], alternative methods may be advantageous in terms of structural resolution, process simplicity, and the absence of resist residues [ 21 ]. We have fabricated ferromagnetic nanodisks on a conventional TEM grid from TedPella ® using three different fabrication methods.…”

“…The third method, stencil lithography, makes use of a shadow mask, which was fabricated by milling submicrometer apertures on a conventional TEM grid using a focused ion beam. This method avoids the resist-based fabrication, which is common in preparing nanodisk samples for TEM [ 8 , 20 ].…”

Two-Step Resist Deposition of E-Beam Patterned Thick Py Nanostructures for X-ray Microscopy

“…Thus, in order to take advantage of the MTXM technique, it is mandatory to use membrane substrates with low X-ray absorption. In particular, the membranes must be thin enough to let through a considerable amount of light, since a large signal-to-noise ratio is crucial for these transmission measurements [11]. Then, completing the patterning process on top without damaging them becomes a challenge.…”